Background: Lactation is thought to buffer stress reactivity via oxytocin (OT). Dysregulation of the HPA axis has been reported in women with postpartum depression (PPD). The co-occurrence of PPD and lactation failure suggests that abnormalities in OT signaling may play a role in PPD. We hypothesized that abnormal OT signaling is implicated in dysregulated HPA axis reactivity among postpartum women with mood symptoms. In a prospective perinatal cohort, we tested associations between OT levels during breastfeeding and stress reactivity.
Methods: We recruited 52 pregnant women who intended to breastfeed, among whom 47 underwent a standardized stressor, the Trier Social Stress Test (TSST), at 8 weeks postpartum. 39 were breastfeeding at time of TSST. We assessed mood symptoms using validated instruments and defined as symptomatic women with EPDS ≥ 10 and/or Spielberger ≥ 34. Following IV placement for blood draws, women breastfed their infants and then underwent the TSST. Mothers' hormone responses were quantified.
Results: Among symptomatic breastfeeding women (N=11; asymptomatic N=28), we found lower OT levels during breastfeeding (p<0.05) and higher CORT levels (p<0.05) both during breastfeeding and the TSST, as compared to asymptomatic breastfeeding women. In a mixed effects model examining CORT reactivity by symptom group and OT AUC, we observed a paradoxical response in symptomatic breastfeeding women during the TSST (group × time × OT AUC p<0.05); higher OT AUC was associated with higher CORT.
Conclusions: In all breastfeeding women, the surge of OT during feeding appears to buffer subsequent stress-induced CORT secretion. However, in symptomatic breastfeeding women, we found a positive correlation between OT AUC and CORT, instead of the expected negative correlation, which we found among asymptomatic women.
Keywords: Cortisol; HPA axis; Lactation failure; Oxytocin; Pospartum depression.
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